Our latest photodissociation dynamics paper has been published in PCCP. The new paper describes ion imaging and photofragment excitation spectroscopy experiments exploring the photochemistry of acetone. We identify ketene as a new primary photoproduct following excitation to S1 and suggest that a roaming mechanism may be responsible. The radical channel forming methyl and acetyl is characterized over a broad range of wavelengths and is dominated by dissociation on the T1 surface following intersystem crossing. Time-resolved measurements using a ps laser system at 266 nm, find an intersystem crossing rate that is surprisingly around six times slower than in acetaldehyde.
You can read the paper here: 10.1039/c7cp07320h
Congratulations to Liz, who successfully defended her PhD dissertation last week despite the best efforts of an antique laptop to derail her talk. The defense was concluded with the conferral of her ceremonial tool belt. It was also great to see Ben again, who belatedly received his. We also said farewell to Liz this week. Liz moves to New England, where she will begin a post-doctoral position at MIT, working with Profs. Bob Field and Christopher Cummins. We wish her every success in her new job!
We are delighted to welcome high school teachers Larry Sepulveda (Rosemead High School) and Linda Kazibwe-James (Whittier Christian School) to the group. Larry and Linda are participating in our NSF-funded ‘Teacher in Residence’ outreach program this year, and will be working with us in the lab for the next month. The program aims to provide high school teachers with hands-on experience of life in a research laboratory.
Many congratulations to Liz, whose work has been recognized with the award of the E.K.C. Lee Fellowship. The Lee Fellowship is named after Prof. Ed Lee, one of the department’s founding faculty members and is awarded “to support outstanding students in chemistry.”
Our latest paper, exploring the photochemistry of acetaldehyde to form CH3 + HCO across a broad range of wavelengths, has been published in PCCP. We used a combination of time-resolved ion imaging, with nanosecond and picosecond pulsed lasers, and photofragment excitation action spectroscopy to identify three distinct dissociation mechanisms. At long wavelengths, dissociation occurs statistically on the S0 surface after many tens of nanoseconds. Dissociation at intermediate wavelengths is dominated by relatively fast dissociation on the T1 surface, leading to fast-moving CH3 radicals. At short wavelengths, a new pathway opens that is assigned to dissociation on the S0 surface, accessed via a conical intersection.
The article can be accessed here: 10.1039/c7cp02573d
This article was selected as part of the 2017 PCCP HOT Articles themed collection.
Our building, Rowland Hall, was dedicated as a National Historic Chemical Landmark by the ACS on April 18th, in recognition of the Nobel Prize-winning work performed there by Sherry Rowland and Mario Molina that identified the role of chlorofluorocarbons in stratospheric ozone loss. A two-day symposium was held at the Beckman Center on April 18th–19th to mark the occasion, featuring distinguished guest speakers from academia, and local AirUCI contributions. Kara and Saswata Roy from Prof. Filipp Furche’s group gave a great joint TED-style presentation explaining how a combination of experiment and theory can provide insights into molecular photochemistry.
On May 12th, we attended the 34th Informal Symposium on Kinetics and Photochemical Processes in the Atmosphere held at UCSD. I gave a talk describing some of our work on the reactions of Criegee intermediates with trace atmospheric gases, Sara presented a poster on the same, and Kara
loitered networked. Aside from learning some exciting new science, we also discovered that the tacos at Puesto in La Jolla are excellent.
Finally, we bade a fond farewell to Ben who has moved on to pastures new. This month he begins a post-doctoral position at Lawrence Berkeley National Lab, working with Dr. Oliver Gessner and Prof. Steve Leone in the Ultrafast X-Ray Science Laboratory. We wish him all the best in the Bay Area and have no doubt that he will be tremendously successful there.
We have been awarded $396,693 by the Chemistry Divison of the National Science Foundation for a three-year project titled, “Unravelling Unconventional photochemistry using time- and state-resolved imaging.” The grant will support our fundamental photochemistry research, in which we use velocity-map ion imaging to explore ‘unusual’ photochemical mechanisms in small molecules.
Our new paper published in J. Phys. Chem. A uses PHOtoFragment EXcitation (PHOFEX) spectroscopy to pick apart the first absorption band of OCS, the most abundant sulfur-containing molecule in the atmosphere. The PHOFEX spectra obtained probing electronically excited S(1D) and ground state S(3P) atoms are distinctly different; the former is broad and unstructured, while the latter shows distinct resonances that can be attributed to vibrational structure following direct excitation of a quasi-bound triplet state.
The article can be found here: 10.1021/acs.jpca.6b06060
Our new paper on the kinetics of reactions between the simplest Criegee intermediate, CH2OO, and the inorganic acids HCl and HNO3 has been published as a “hot paper” in Angewandte Chemie International Edition. The reaction with HNO3 in particular is likely to be an important sink in polluted environments. You can read it here: 10.1002/anie.201604662
UPDATE: A news article highlighting our paper has been published on ChemistryViews.